Electrochemical cells, or batteries, are commonly used as electrical energy sources. A battery contains a negative electrode, typically called the anode, and a positive electrode, typically called the cathode. The anode contains an electrochemically active anode material that can be oxidized. The cathode contains an electrochemically active cathode material that can be reduced. The electrochemically active anode material is capable of reducing the electrochemically active cathode material. A separator is disposed between the anode and the cathode, and an ionically conductive electrolyte solution is in intimate contact with the cathode, the anode, and the separator. The battery components are disposed in a can, or housing, that is typically made from metal.
When a battery is used as an electrical energy source in an electronic device, electrical contact is made to the anode and the cathode, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide electrical power to the electronic device. The electrolyte contains ions that flow through the separator between the anode and cathode to maintain charge balance throughout the battery during discharge.
There is a growing need to make batteries that are better suited to power contemporary electronic devices such as toys; remote controls; audio devices; flashlights; digital cameras and peripheral photography equipment; electronic games; toothbrushes; radios; and clocks. To meet this need, batteries may include higher loading of electrochemically active anode and/or cathode materials to provide increased capacity and service life. Batteries, however, also come in common sizes, such as the AA, AAA, AAAA, C, and D battery sizes, that have fixed external dimensions and constrained internal volumes. The ability to increase electrochemically active material loading alone to achieve better performing batteries is thus limited.
The composition of the anode is a design feature that may be adjusted in order to provide increased performance. For example, a surfactant can be included in the anode composition to create a protective layer around the zinc particles to inhibit a zinc corrosion reaction and the formation of hydrogen gas that can occur when the cell comprising the anode is at rest. The surfactant can adhere to the surfaces of the zinc anode particles, inhibiting hydroxide ions or water from approaching the zinc particles, thereby suppressing the corrosion of the zinc and the formation of hydrogen gas (reactions (I) and (II)) from taking place on the surfaces of the zinc particles.Zn+4OH−→Zn(OH)42−+2e−  (I)2H2O+2e−→2OH−+H2  (II).Phosphate ester based surfactants are commonly used in the industry; however, this class of materials is commonly regarded as harmful to aquatic life forms and can be listed as a carcinogenic, mutagenic, or reprotoxic (CMR) material. Additionally, a commonly used phosphate ester material includes a nonylphenol functional group, which has regulated use in some countries due to health and environmental concerns.